Transportation of pressurized chemicals is usually conducted through pipelines or by tanker vehicles. When tanker vehicles, such as tanker trucks, tanker aircraft, or tanker ships, move pressurized chemicals from an origin to a destination, the pressurized chemicals must be uploaded to the tanker vehicle at the origin and downloaded from the tanker vehicle to a storage device at the destination. Generally, a pipeline arrangement is used to transfer chemicals from or to the tanker vehicles, with the pump or compressor providing power to move the chemicals from one point to another.
Transportation of pressurized chemicals is particularly prevalent in the liquid petro-chemical industry, more particularly, in the propane, anhydrous ammonia, and liquefied natural gas (LNG) industry. Local and national regulations dictate that storage tanks for the liquefied chemicals, whether stationary or vehicle mounted, must have self-closing stop valves to prevent unintentional leaking of the chemicals to the environment.
In the propane industry, the stop valves are typically mounted at least partially within the storage tank (e.g., the valve inlet is disposed within the storage tank). Such a mounting scenario is possible because of the single wall tanks used to store the propane.
Liquefied natural gas and other cryogenic temperature (−238° F./−150° C. or less) chemicals are usually insulated with double wall storage tanks due to the low temperatures. The traditional stop valves cannot be attached to these liquefied natural gas tanks because of the insulation requirements. As a result, gate valves or ball valves are typically mounted in-line with transportation piping in liquefied natural gas systems. While these gate valves or ball valves can adequately perform a shut-off function during a fire, they lack an automatic shutoff capability when there is leakage downstream of the valve due to pipe failure. They also lack an automatic pressure equalizing capability for vaporized gas that gets trapped downstream of the valve.
Finally, ball and gate transfer valves for liquefied natural gas storage tanks must include heavy protective cages to prevent inadvertent loss of gas in a spill because of valve or pipeline failure in the case of external impact or accidents (such as tank rollover) that may affect valve integrity. These heavy protective cages are regulatory safety requirements.